The invention is in the field of photoflash arrays. U.S. Pat. No. 4,133,023 to Hanson discloses a photoflash array, of the Flip Flash type, having a reflector unit configured to provide a plurality of individual reflectors having raised radiation barriers between adjacent reflectors to prevent "sympathetic" flashing of lamps due to heat and/or light from an adjacent flashing lamp. An economical way of manufacturing the reflector units is to pressure-form heated plastic sheet material, such as with a mold and a vacuum and/or air pressure. The reflector unit is generally rectangular, and the individual reflectors and radiation barriers are transversely oriented along the length of the unit. The radiation barriers have a tapered configuration so that the reflector units can be stacked in a nested manner for compact storage prior to being used in manufacturing flash arrays. Some manufacturing difficulties have been incurred due to the stacked reflector units sometimes sticking together so tightly, because of the nested tapered radiation barriers, that it is difficult to remove the top unit, such as by a vacuum lifting arm, for positioning it into a flash array. The above-referenced patent application discloses and claims a solution to this problem, in the form of ribs provided in the rear concavities of the radiation barriers.